Suppose that you are hooked up to a button which, if pressed, will induce in you a desire for a flash of green light followed by a flash of green light. Plausibly, if you will have a desire for something neutral or good, that gives me a reason to fulfill that desire. Assume that you consent to my pressing the button as well as to my not pressing it, but you have no desire either way. I now press the button, on the grounds that:
- you will have a desire to see a green flash, and by pressing the button I will have fulfilled that desire of yours.
Another case. Normally, if I know that I will make you a promise, that gives me a reason to do something that makes me able to fulfill of that promise. Suppose now that I am deliberating whether to promise you to draw a pig. Standing by is Jim, who I know will hand me a piece of paper and a pink crayon if and only if he hears me promise to you that I will draw a pig. So I promise you to draw a pig on the grounds that:
- I will shortly be subject to a promise to draw a pig, and by making the promise I make myself able to fulfill the promise, as Jim will supply me with the wherewithal.
Now a third case. A couple has a child on the basis of the thought that if someone exists or will exist, then one has reason to provide them with a good, and
- The child will exist, and by procreating we will be providing the child with various goods, including especially life.
If this is right, then one cannot procreate for the child's sake.
One may be able to procreate in order that the world contain the good of the child's life, but that is an impartial good, not a good to the child. (And there are some Kantian worries about this—it seems to make of the child a means.)